Nearly two-thirds of Britain's prisoners are being held in overcrowded jails, according to the findings of a new study.

The Howard League for Penal Reform says 52,500 people are in jails running above capacity.

In some instances, prisons are holding almost double the number of recommended inmates.

Worst is HMP Preston with 661 prisoners - but only 356 places.

Director of the Howard League, Frances Crook, has called on the government to include a compulsory limit on the prison population in the Criminal Justice Bill, which is due to be published later this year.

She said: "Our prisons are becoming no more than warehouses once again.

"The consequences of overcrowding are jeopardising both the safe running of the prison system and the rehabilitation of individual offenders.

Most overcrowded jails

Preston 661 prisoners (356 places)

Shrewsbury 331 (184)

Dorchester 258 (153)

Swansea 364 (219)

"If prison is to serve any useful purpose it must be to return prisoners to the community better equipped to lead crime-free lives.

"The current crisis effectively precludes this."

The prison population currently stands at 71,471 and is beginning to climb after a drop of several hundred earlier in the summer.

This rise goes against the normal summer-time pattern of an overall fall in the number of inmates.

Prison numbers have spiralled from 45,500 in June 1992, and have jumped 6,000 since the start of the year.

Overall, 64 jails are now overcrowded, said the charity.

The figures are taken from the Home Office research, development and statistics directorate.

The occupancy figures relate to the number of prisoners jails were built to hold.

Review promised

Prisons Minister Hilary Benn said the current level of overcrowding was
undesirable, but very limited.

He said only 20 per cent of prisoners were currently having to double up in a cell designed for one.

Mr Benn said: "Regimes are still being delivered, and prisoners are still receiving education, purposeful activity, offending behaviour programmes, and getting exercise and time out their cells.

Benn: 'We are reviewing the situation'

"The government rejects the idea of a statutory limit on the prison
population.

"No prison is being required to take more than its operational capacity and we are committed to ensuring that overcrowding does not impact on safety in any way, and we recognise the pressures it creates for prisoners and staff."

Mr Benn said a review would examine management of the prison population.

He added that the Prison Service planned to increase its capacity by about 1,100 places by the end of October, with a further 1,200 places by March next year.

The Howard League believes that, although 20 per cent of inmates are "doubling up" in cells designed for one, the Prison Service does not collect data on overcrowding in other types of cells, such as when three inmates have to share facilities designed for two.